FIG. 2 is a schematic block diagram of conventional CNC equipment.
In FIG. 2 reference numeral 1 indicates a microprocessor unit (MPU), which controls the operation of the entire equipment and is connected to respective sections via a bus 2 including an address bus, a data bus and a control bus. Programs necessary for the MPU 1 to perform predetermined functions are stored in a read-only memory (ROM) 3 and machining programs necessary for NC machining are stored in the form of a punched tape or memory in an external storage 4. The MPU 1 reads these data via the bus 2 and controls a first axis servo system 51, a second axis servo system 52, . . . to thereby perform required NC machining.
For example, in the first axis servo system 51, a position command issued from the MPU 1 for a first axis is provided via the bus 2 to a first axis position control circuit 61. The first axis position control circuit 61 responds to the position command to generate a feedrate command signal for a first axis motor 71. The first axis motor 71 rotates on the basis of the feedrate command, shifting the position of a tool or machining table in the first axis. The amount of change in the position of the tool or machining table thus moved is fed back to the first axis position control circuit 61, which effects control so that a residual error in position in the first axis is held at a predetermined value, thereby performing position control in the first axis.
Position control in a second axis in the second axis servo system 52 is also effected in exactly the same manner as described above.
With such conventional CNC equipment as depicted in FIG. 2, control in each axis is performed independently in response to a position command, but the traveling speed or feedrate in each axis in this case cannot be known, so that it is impossible to obtain an output indicating the actual feedrate of the machining table.
On the other hand, conventional laser machining under NC control employs a fixed beam intensity in many cases; therefore, when the feedrate of the machining table is low, the machining energy per unit area increases and large holes are drilled, whereas when the feedrate of the table is high, holes machined are small. Accordingly, holes of a fixed size cannot be obtained.
It is therefore desirable that holes can be made in a fixed size by controlling the beam intensity in accordance with the feedrate of the machining table, but the conventional CNC equipment cannot provide the feedrate of the machining table as mentioned above, and hence is incapable of controlling the beam intensity.